A conventional television system, such as a system in accordance with the NTSC broadcast standard adopted in the United States and elsewhere, processes a television signal representative of an image with a 4:3 aspect ratio (the ratio of the width to the height of a displayed image). Recently, there has been interest in using higher aspect ratio images for television systems, such as 5:3, 16:9 and 2:1, since such higher aspect ratios more nearly approximate or equal the aspect ratio of the human eye compared to the 4:3 aspect ratio of a standard television display. Advanced television systems for producing 5:3 aspect ratio images are described, for example, in U.S. Pat. No. 4,816,899--Strolle, et al. and in U.S. Pat. No. 4,855,811--Isnardi. In these systems side panel image information is encoded by time compressing low frequency side panel luminance and chrominance information into horizontal overscan regions, and high frequency side panel luminance and chrominance information are encoded by time expansion and modulation of an auxiliary subcarrier. The side panel luminance information component (Y) and the side panel chrominance color difference information components (I and Q) are each processed separately before being encoded.
The auxiliary subcarrier, modulated by the high frequency side panel luminance and chrominance information, phase alternates from field-to-field, and is located within the frequency spectrum occupied by baseband composite video. In order to insure that this signal does not cause objectional interference in the compatible NTSC signal, it is attenuated relative to other components of the encoded signal. However if this signal is sufficiently attenuated to preclude any observable interference in the compatible NTSC signal, an undesirable result may occur in the widescreen receiver. Because these components are attenuated relative to other components of the widescreen television signal, on detection at the widescreen receiver they exhibit a poorer signal-to-noise ratio. Consequently, when the center and side panel signals are recombined, the seams where the center and side panel information are joined may be objectionally made evident by differences in the noise content between the center and side panel images.